The ECMAScript specification defines Use Strict Directive, but allows implementations to define their own directives. From here :
Implementations can define specific implementation values for ExpressionStatement, which are not a strict directive and which are found in the directory prolog.
What are the famous implementation directives? A quick Google search does nothing but use strict .
use strict
I can think of use asm and use strong . Are others being used?
use asm
use strong
For Spidermonkey I only found :
macro(useAsm, useAsm, "use asm") macro(useStrict, useStrict, "use strict")
V8 same source :
F(use_asm, "use asm") F(use_strict, "use strict")